Among conventional liquid crystal display elements, a twisted nematic (TN) mode liquid crystal display element (LCD) that uses a liquid crystal having a positive dielectric anisotropy, for example, has been put into practical use. This TN mode LCD is driven by applying an electric field in a direction perpendicular to the substrate surfaces to change the orientation of the liquid crystal molecules such that their long axes are parallel to the direction of the electric field.
In recent years, along with improvement in definition, progress has been made in reducing the size of pixels. However, with reduction in the size of pixels, the influence of a transverse electric field generated during voltage application between bus lines (electrode wiring) in the vicinity of the edges of the pixel electrodes has become a problem. In a conventional LCD, while it is common, for preventing coloration, to orient the liquid crystal molecules at a low pretilt angle using a common orientation film, this makes pixels susceptible to the influence of a transverse electric field from adjacent pixels, thereby inviting alignment defects such as reverse tilt. Alignment defects are particularly noticeable in the perimeter portions of pixel regions, and these alignment defects bring about disclination at the boundaries between the perimeter portions and regions other than the perimeter portions. Thus, in a conventional TN mode LCD, the problem of degradation in display characteristics, such as a decrease in contrast and the like, results.
In order to prevent reverse tilt caused by the transverse electric field from other pixels, the polar anchoring energy of all regions of the pixels has been increased. However, the influence of the transverse electric field in pixel regions other than the perimeter portions is small, and when the polar anchoring energy is large in these regions, coloration arises.
Transverse electric field-driven liquid crystal display elements provided with counter electrodes on a substrate surface have also been developed.
For example, in order to obtain a wide-viewing angle, in-plane switching (IPS) mode LCDs, which switch the liquid crystal molecules in a direction within the plane of the substrates by applying a so-called transverse electric field in a direction parallel to the substrate surfaces, have been developed. In the area above the electrodes in IPS mode LCDs, a transverse electric field is not generated, but rather an electric field is generated in a direction perpendicular to the substrate surfaces. For this reason, the alignment state of liquid crystal above the electrodes cannot be changed. When an electric field is applied in an IPS mode LCD, the liquid crystal layer comes to have both a region in which molecules transition to a new alignment state and a region in which molecules remain in the initial orientation state. As a result, the alignment state of the liquid crystal deteriorates, especially around the boundaries of these regions. Thus, IPS mode LCDs are disadvantageous in that response speed is even slower than that of conventional vertical electric field mode LCDs.
In addition, in IPS mode LCDs, orientation films having the same anchoring energy are provided on opposing substrates. In such an LCD, liquid crystal molecules above the substrate having electrodes on its surface rotate to at most approximately 90° when driving is ON. On the other hand, liquid crystal molecules above the substrate without electrodes on its surface hardly rotate. Thus, sticking (phenomenon wherein liquid crystal molecules to not return to the initial orientation state when driving is switched from ON to OFF) occurs, resulting in degradation in the visual characteristics of the liquid crystal display element.
As is described above, liquid crystal display elements operated in twisted nematic (TN) mode, which use a liquid crystal having a positive dielectric anisotropy, those operated in IPS mode, which have a very wide viewing angle and whose the liquid crystal molecules are driven within a plane using transverse electric field, and the like have been put into practical use.
In contrast to these, a bend alignment-type liquid crystal display element has been proposed which utilizes a change in refractive index caused by the change in the rise angle of each liquid crystal molecule in a state wherein the liquid crystal molecules between the substrates show a bend alignment (OCB mode liquid crystal display element). Compared to the speed of the change in alignment between an ON state and an OFF state in a TN liquid crystal display element, the speed of change in alignment of each of liquid crystal molecules showing a bend alignment between an ON state and an OFF state is very high, making it possible to obtain a liquid crystal display element with an excellent response. The bend alignment-type liquid crystal display element described above is self-compensating in terms of optical retardation because all of the liquid crystal molecules between the upper and lower substrates show bend alignment, and the display element enables a wide viewing angle at low-voltage operation due to a film retardation plate that compensates for retardation.
The liquid crystal display element described above is usually fabricated so that the liquid crystal of the liquid crystal layer shows a splay alignment when voltage is not being applied. Therefore, in order to utilize the bend alignment to change the refractive index, it is necessary to uniformly transition the entire display portion from a splay alignment state to a bend alignment state. The transition to a bend alignment proceeds with transition seeds as the center. The location of transition seed generation is not regular, appearing, for example, at orientation irregularities or damaged areas of the orientation film interface. Because the location of transition seed generation is not fixed, display defects tend to arise. Therefore, it is very important to uniformly transition the entire display portion from a splay alignment to a bend alignment before use.
In addition, although a high driving voltage is needed to transition from a splay alignment state to a bend alignment state, it is difficult to easily bring about this transition in alignment state because the driving voltage is generally limited.
Furthermore, the perimeter portion of the display region of a liquid crystal display element does not contribute to liquid crystal display. Thus, it is not necessary to inject liquid crystal into the perimeter portion of the display region. However, in conventional liquid crystal display elements, liquid crystal injected into the perimeter portion of the display region is wasted, as it is difficult to inject the liquid crystal without also injecting the liquid crystal into the perimeter portion of the display region.
Finally, use of orientation films having more than one liquid crystal orientation has been proposed in order to improve the display characteristics of liquid crystal display elements. However, further improvement in display characteristics is needed beyond what has been realized by such methods.